An optical page composer is a matrix or array of cells, each cell acting as a light valve which passes light vel non according to the binary state of the cell. The page composer is best used in an holographic memory system. For writing into the storage medium or memory, a coherent light beam from a laser impinging on the page composer emerges in a moldulated pattern as an object beam carrying an optical equivalent of the information that is stored in the page composer. This object beam is caused to interfere with a write reference beam at some location of the storage medium, e.g., thermoplastic film, where the information is stored in holographic form as a single page of information.
The information that is stored in each page of the storage medium can be read out from the memory system by illuminating the page in the storage medium by a read reference beam. If the direction of the read reference beam is conjugate to that of the coherent light beam, i.e., the write reference beam, a real image will be formed on the page composer or a symmetrical position on either side of the storage medium by reflective diffraction. An array of photosensors, an array of memory storage cells and an array of light valves, i.e., the page composer, can be superimposed to form a latrix (light accessable transistor matrix - see the publication "Promise of Optical Memories," J. A. Rajchman, JAP, Volume 41, No. 3, Mar. 1, 1970, pp. 1376-1383). The latrix is then a main memory whose contents may be manipulated by a central processor; when additional storage of data or data is required, the contents of the latrix may be "photographed" instantly into a holographic record for storage in the storage medium and new information may then be brought into the latrix. See the D. S. Lo, et al, U.S. Pat. No. 3,761,155 for an holographic memory system incorporating an electrically alterable page composer utilizing bubbles as the light valves.